1. Field of the Invention
The present invention relates to a radio equipment, and more particularly to radio equipment including a compensator for compensating for an orthogonality error between a real-axis signal and an imaginary-axis signal of a signal expressed as a complex number.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. P10-56484 discloses a conventional receiver which employs a characteristic compensator for compensating for orthogonal/amplitude errors occurring in received signals owing to incompleteness of an apparatus.
In radio equipment including such a receiver as disclosed by the Japanese Publication, an orthogonality error of a complex signal caused by a dispersion or all characteristics of an analog processing section in mixers (frequency converters) which process RF (Radio Frequency) band of the radio equipment, such as an orthogonal modulator (a mixer having an input of a complex signal and an output of a real signal), an orthogonal detector (a mixer having an input of a real signal and an output of a complex signal), or a mixer having an input of a complex signal and an output of a complex signal, may appear as an image signal which does not exist in an ideal signal. Accordingly, in order to transceive signals without distortion, conventional radio equipment may employ a compensator for compensating for an orthogonality error of a complex signal.
However, in recent radio equipment, as the frequency of RF signal increases and system bands become wider, it is difficult to obtain a necessary degree of image suppression even if a mixer with a high image suppression effect is used. Further, since research for obtaining not only characteristic compensation of a mixer but also the necessary degree of image suppression by suppressing an image frequency signal in a RF filter, a high intermediate frequency has been necessary for a radio processing section.
Accordingly, as a conventional receiver shown in FIG. 17, when an output of an orthogonal detector 2 is sampled by ADCs (A/D converters) 3 and 4, a characteristic compensation process of the orthogonal detector 2 is performed by a characteristic compensator 50 through a digital signal processing, the compensated signal is frequency-converted by a frequency converter 51 so that an immediate frequency can be low, the converted signal is converted to a signal with low sampling frequency by a decimator 52, and the converted signal is demodulated by a detector 8, processing a high IF frequency in the output of the orthogonal detector 2 implies that a high sampling frequency is necessary when a sampling is performed. Further, in order to perform the characteristic compensation process of the orthogonal detector 2, the consumption power of characteristic compensator 50 becomes much greater.
Further, even in a case in which a characteristic compensation is performed by means of an analog circuit without conversion into a digital signal, it is difficult to secure sufficient accuracy in a passive circuit in order to perform a compensation with high accuracy in a higher frequency, and it is necessary to increase consumption power in an active circuit in order to maintain high frequency.